Box 3: Greenhouse Gases

The six main greenhouse gases are

• Carbon dioxide (CO2)
• Methane (CH4)
• Nitrous oxide (N2O)
• Hydrofluorocarbons (HFCs)
• Perfluorocarbons (PFCs)
• Sulfur hexafluoride (SF6)

Because GHGs vary in their ability to trap heat in the atmosphere, some are more harmful to the climate than others. Each GHG has a “global warming potential,” or“GWP,” which refers to its heat-trapping ability relative to that of carbon dioxide (CO2). For example, CO2 is the most prevalent GHG, but methane (CH4) is 21 times more potent, thus the GWP of methane is 21. (1) GHGs are often reported as CO2-equivalents (CO2e).

Notes

1. Intergovernmental Panel on Climate Change (IPCC), “Climate Change 1995: The Science of Climate Change.”